1. Field of the Invention
The invention relates to a method of connecting a terminal and an electric wire, which connects the terminal to be connected to, for example, a car panel or an engine block and the an electric wire supplying an earth current.
2. Related Art
As one of examples of a related art concerned with this kind of connecting method of the terminal and the electric wire, known are those shown in FIGS. 5 and 6 (See Japanese Patent Publications Nos. JP H11-86921A and JP 2000-285983A.).
As shown in FIG. 5, a first related art (Japanese Patent Publication No. JPH11-86921A, pp. 2 to 4 & FIG. 7) lessens invasion of a sealing material 58 into a wire connection part between a core wire portion 57a and the terminal 50 for realizing stable electrical connection, and closing an electric wire insertion hole 53 of a small diameter pipe 52 with the core wire portion 57a. 
A terminal 50 is made by connecting through forcing to press a small diameter pipe 52 into a large diameter pipe 51 being different in diameter or welding both, and has a wire connection part 55 at one side and an electric contact part 56 at the other side. Both sides are opened, and an electric wire 57 is inserted into one opening end of the small diameter pipe 52, while a water tight member 54 is inserted into the other opening end of the small diameter pipe 52.
An inner diameter of the small diameter pipe 52 is formed to be somewhat larger than an outer diameter of the electric wire 57, and a border between an insulation covering portion 57b and a core wire portion 57a is positioned at the inside of the small diameter pipe 52, and if tightening a tubular wall of the small diameter pipe 52, the electric wire 57 is closely adhered to the inside of the small diameter pipe 52. The water tight member 54 is an elastic plate rubber, and if pressing the other opening end of the small diameter pipe 52 from an direction of a plate thickness of the water tight member 54, the electric wire 57 and the small diameter pipe 52 are held leaving no space.
Subsequently, a sealing material 58 is poured into an opening of the large diameter pipe 51, and a waterproof is provided at a connection between the electric wire 57 and the small diameter pipe 52. Being under the condition of no space between the electric wire 57 and the small diameter pipe 52, the sealing material 58 does not flow into a side of the small diameter pipe 52.
As shown in FIG. 6, a second related art (Japanese Patent Publication No. JP 2000-285983A, pp. 2 to 3 & FIG. 2) provides a complete waterproof in a wire connection part 62 of a terminal 60 by closely adhering a heat shrinkage tube 63 over the wire connection part 62.
A terminal 60 comprises an electric contact part 61 shaped in a round plate and a wire connection part 62 having pairs of front and rear crimping pieces 62a, 62b. The electric contact part 61 is formed with a bolt (not shown) insertion hole 61a for connecting to a car body. The front crimping piece 62a of the wire connection part 62 is crimped with a core wire portion 65a of the electric wire 65, while the rear crimping piece 62b is crimped with an insulation covering portion 65b of the electric wire 65. The wire connection part 62 is closely covered over with the heat shrinkage tube 63 coated on an inner circumference with an adhesive agent such as a hot melt.
However, the above mentioned prior methods of connecting the terminal and the electric wire are involved with problems to be solved, as follows.
In the first related art, the terminal 50 is composed by connecting the large diameter pipe 51 and the small diameter pipe 52, and for connecting the terminal 50 and the electric wire 57, the plate rubber as the water tight member 54 and the sealing material 58 are necessitated, resulting in increasing the number of parts and members and heightening cost, accordingly.
As the connection between the large diameter pipe 51 and the small diameter pipe 52 is conducted by press fitting or welding, there arises a problem that the operation is troublesome. Besides, it is possible that the connection portion does not have sufficient sealing condition due to welding defects, or pressure shortage during connecting operation by press fitting. In such the case, there is a fear that the sealing material 58 injected from the opening of the large diameter pipe 51 could leak out.
Further, since the tubular wall of the small diameter pipe 52 is tightened under the condition that the border between the insulation covering portion 57b and the core wire portion 57a is positioned at the inside of the small diameter pipe 52, it is difficult that the core wire portion 57a and the inside of the small diameter pipe 52 are closed, causing fear of poor contact.
The second related art heats the shrinkage tube 63 to a predetermined temperature to reduce the size thereof in order to cover the wire connection part 62 of the terminal 60 for attaining the waterproof and an insulation, but since rate of shrinkage is decided depending on sizes or material qualities, those should be used properly, and a problem is present in a connection workability being inferior.
In case the heat shrinkage tube 63 is used on the inside with the hot melt as an adhesive, owing to heating of the wire connection part 62, the hot melt is heated and melts (a softening temperature is around 80° C.), and the waterproofing property of the heat shrinkage tube 63 might be spoiled. Particularly, in the case that an aluminum electric wire is connected to the terminal 60, contact resistance becomes higher by formation of an oxidized film at the connection portion. As a result, the connection portion could be abnormally heated more easily, thereby causing a melting of the hot melt adhesive.